In Japan at present, the amount of waste paper, including broke for regeneration, used as a material for producing paper and paper board exceeds 50% of the total production materials and already occupies the position of a main material.
Waste papers which can be pulped again include newspaper corrugated containers, magazines, printed woodfree, color printed wood free paper (including art paper), white shavings, cards, high grade white wood containing shavings, white wood containing shavings, white manila, tickets, high grade wood containing waste, brown printed woodfree, chipboard cuttings, carton box waste, thermosensitive paper, pressure-sensitive duplicating paper and CPO (computer printout).
These waste papers are generally pulped again through a defiberizing process in which the waste Papers are defiberized and a pulp suspension is obtained, a coarse screening process in which foreign matters are separated from the pulp suspension, a fine screening process, a deinking process in which printing ink is removed, a bleaching process for whitening, etc. However, waxed paper, pressure-sensitive adhesive paper, paper coated with a hot-melt agent, etc. are discarded or burned at present as "taboos", or waste papers which can never be pulped again, because it is impossible to remove wax, pressure-sensitive adhesive, hot-melt agent, etc. from the pulp fibers.
According to the quality standard of waste papers established by the industry, it is basically improper to mix paper stuff with said waxed paper, pressure-sensitive adhesive paper or paper coated with a hot-melt agent, and they may be mixed only in an unavoidable case in an amount less than 0.3%.
The reason therefor is explained in case of the Pressure-sensitive adhesive paper as follows: The pressure-sensitive adhesive paper contains a pressure-sensitive adhesive as much as 5 to 50%, and it is impossible to remove said pressure-sensitive adhesive from pulp fibers because the adhesive has a large adhesive strength. If a recycled pulp containing the pressure-sensitive adhesive is made into paper, the pressure-sensitive adhesive may clog wires and contaminate a press roll or a felt in a paper-making process, causing problems such as a breakdown and the reduction of paper-making efficiency. Furthermore, there is a fatal problem that the pressure-sensitive adhesive exerts a bad influence upon the forming of a paper layer or the paper quality. For example, the pressure-sensitive adhesive forms spots on the paper surface. Under these circumstances, a method of pulping waste pressure-sensitive adhesive paper has not been tried yet and there has been no literature disclosing said pulping method.
The present invention provides a novel method of obtaining a recycled pulp from waste pressure-sensitive adhesive paper. More particularly, it is an object of the invention to provide a pulping method for effectively separating foreign matters such as pressure-sensitive adhesive, silicone and plastic films and obtaining a recycled pulp having a high brightness even when colored waste paper is included, said recycled pulp being free from operation troubles in the paper-making process and wild formation.